1. Field of the Invention
The present invention relates to an oxide superconductor in which the anisotropies of critical currents and critical magnetic fields resulting from the layer structure of oxide superconductor crystals are reduced in a shaped article comprising an aggregate of oxide superconductor crystals together with a conductive metal.
2. Description of the Prior Art
It has long been known that as some metals or alloys are cooled to the vicinity of absolute zero, their electrical resistance is reduced to zero. This property has been called superconductivity. Recent reports have revealed that certain metal oxide crystals, having the perovskite structure, show such superconductivity at relatively elevated temperatures.
These oxides of the perovskite structure have a transition temperature higher than the boiling point of nitrogen, and are therefore called the "high-temperature oxide superconductors". In view of their high transition temperature, they are now under study to put them to practical use. The superconductivity of such oxides is interesting but it has not been used for any practical conductor because of their critical current density is extremely low.
Since the perovskite high-temperature oxide superconductors are crystals having a layer structure, however, large anisotropies appear in their critical magnetic field Hc.sub.2 and their critical current Jc. In thin-film single crystals, it is seen that there is a certain limitation on the direction of current flow.
In an aggregate of single crystals, therefore, the junction points of single crystals are directionally so random that current flow is impeded. In a polycrystal thin-film, on the other hand, no satisfactory superconductive contact has been achieved at the interfaces of single crystals.
In addition, when the oxide crystal superconductors have been formed into a wire or shield material by sintering, only a very limited superconductive contact area is obtained because, since they are sintered bodies, they are hence, microporous. This porosity interferes with current flow and therefore impedes superconductivity of the formed/shaped products.